Systemic infection in Atlantic salmon Salmo salar with a Dermocystidium-like species

Abstract

A chronic mortality in subadult Atlantic salmon Salmo salar reared in California was caused by systemic infections with a Dermocystidium-like species. Parasitic cells occurred primarily at the periphery of granulomas in the kidney, liver, spleen and testes. Actively replicating vegetative stages 2 to 7 pm in diameter were also found withln melanomacrophages of the kidney. These stages contained a dense granular cytoplasm with osmiophilic inclusions, a nucleus with an indishnct nucleolus and were surrounded by thick, Periodic-Acld-Schiff-positive cell walls. The parasite induces a similar disease and has structural affinities to Dern~ocystidium spp. described as causes of systemic infections in salmonids in Europe.

Infection of juvenile salmon Salmo salar with a Dermocystidium-like organism in Sweden

“…Thus, in some respects the present organism resembled the systemic Dermocystidium in the internal organs of salmonids that was described by Nash et al (1989), but also to some extend the visceral agent of salmon described by McVicar & Wootten (1980). Furthermore, it was PASpositive like the systemic Dermocystidium infections of salrnonids described by Hedrick et al (1989) and Nash et al (1989). However, in the Dermocystidium described by Hedrick et al (1989), a prominent vacuole was not found.…”

“…Furthermore, it was PASpositive like the systemic Dermocystidium infections of salrnonids described by Hedrick et al (1989) and Nash et al (1989). However, in the Dermocystidium described by Hedrick et al (1989), a prominent vacuole was not found. The parasite observed in salmon in our study also had similarities to D. salmonis in the choice of host species and predilection site.…”

“…Dermocystidium species are often parasitic of young or juvenile fish and infection usually commences when water conditions are cold. Disease outbreaks have been associated with fish mortalities (Pauley 1967, Allen et al 1968, McVicar & Wootten 1980, Hedrick et al 1989, Nash et al 1989.…”

Systemic granuloma in goldfish caused by a Dermocystidium-like aetiological agent

“…; Perkins 1974). Ultrastructural affinities of the integumental D. salmonis as reported recently by Olson et al (1991) are convincingly different from the causative agent, also named Dermocystidium, of the salmonid systemic granulomatosis as described by Van de Moer et al (1986) and Hedrick et al (1989).…”

“…The presumed aetiological agent detected in goldfish affected by visceral granuloma was very similar to Dermocystidium macrophagi or the Dermocystidium-like organisms which cause a similar systemic granulomatous disease in salmonids (McVicar & Wootten 1980, Van de Moer et al 1986, Hedrick et al 1989) and in carp (Kovacs-Gayer et al 1986). Organisms similar to those presently reported from goldfish were detected in granuloma-affected goldfish in the USA, and following light and electron microscopic study were regarded as hartmanellid amoebae (Voelker et al 1977).…”